Cracking and distillation of oils



Sept. 28, 1943. A M. THOMSEN 2,330,760

' I v CRACKING AND DISTI LLATION 0F OILS 7 Filed Sept. s, 1959 2 Sheets-Sheet 1 I f u H. when crawm Vapor: ,Lmdded Tatimnv mama me INVEN TOR.

Sept. 28, 1943. A. M. THOMSEN 2,330,760

CRACKING AND DISTILLATION OF 'OILS Filed Sept. 5, 1939 2 Sheets-Sheet. 2

23 CIMIGE OIL IN VEN TOR.

Patented Sept. 28, 1943 UNITED STATES PATENT OFFICE 2,330,760 f CRACKING AND DISTILLATION F olLs Alfred M. Thomscn, SanFranci sco, Calif. Application September 5, 1939, Serial No. 293,314

o1.19s c1) 3 Claims.

The peculiar advantages of cracking the highboiling fractions of petroleum in the Vapor phase,i1"1 the presence of superheated steam has long been known, particularly when the steam is used in such a large excess that it acts as the carrier of all the heat required in the reaction. The advantages are a better yield, a higher 00 tane rating of the accepted perfect elimination of sulphur.

Such being the case, it israther strange that the commercialization of such use of superheated steam has not as yet progressed beyond the embryonic stage in the few instances where its use has been attempted on a reasonably large scale, until we scan the reason for such failures. First among these is the unfavorable heat balance of the steam carrier. With this eliminated there is no reason why such use of superheated steam can not be efficiently used. It is in the means whereby I eliminate this difiiculty that myyinvention more particularly resides.

"fvvithout using exact figures it will be seen that from the standpoint of heat utilization the use of superheated steam is most unsound. To raise one pound of water from say 52 F. to boiling requires 160 B. t. u. To convert the water into steam requires approximately 1000 B. t. u. To superheat said steam to a temperature of say 1200 F., which is about proper, requires another 500 B. t. u., as the specific heat of steam is a little less than /2 that of water. To raise 'a pound of water to reaction temperature, therefore, requires close to 1700 B. t. u.

The critical temperature range for steamin the vapor phase cracking is from an initial of say 1200 F. to only 1000 Rwhen it becomes a very slow'agent, so of this entire input of 1709 B. t. u. only about 100 B. t. u., or rather less than 6% of the total can be used in actual cracking. It is thisunfortunate property of superheated steam which so much mitigates against its use. I will now describe how this difiiculty can be evaded to such a degree that superheated steam becomes an acceptable means of oil cracking.

The process is best considered under two aspects, namely the use made of the sensible heat of the steam in treatment of the oil in certain steps where distillation rather than cracking is the objectafter its temperature is too low for the latter step; and secondly therecuperation of the latent heat of the total vapors in the form of latent heat of evaporation of water in the process of condensing same so that the oil fraction may be separated from the water fraction. A preferred version of my process will next be given which corresponds to and is explanatory of the attached flow sheet and drawing. Considered thusly it will be seen thatthe process consists of 7 separate stages or steps, each of which will now be described in detail. ,lndividv clistillate, and a very ually they are: A cracking stage, a coking stage, a distilling stage, an evaporating stage, a secondary cooling stage, a fractionating stage and a compressor-superheater stage. Collectively they form one process from which issues a low-boiling gasoline fraction, gas and coke as the sole products.

In the first or cracking step, steam with its full quota of superheat is admitted to the surface of a bath of oil, maintained in a state of turbulence in a cracking chamber. There are consequently two actions progressing simultaneously, namely, distillation from the surface of the comparatively cool oil and effective cracking of the vapors thus produced in the hot vapor space above the distilling oil. The relative amount of oil distilled and cracked is thus controllable by regulating the state of turbulence of the bath of oil. It should be noted that the oil "operated upon is not charging stock direct, but a residuum from the third step of the process. It has, therefore, undergone a definite amount of preparation before being admitted to the cracking phase. In the drawing this step is illustrated at B, Fig. 2.

In the second or cooking stage, the residuum from the first stage is completely distilled so that coke is left as a residue. The flow sheet shows the source of heat as the total vapors from the first stage. While these are too cool to perform the cracking stage effectively they are amply hot enough to coke the residuum if same be-properly exposed so as to absorb the available heat. This may be effected in any conventional manner, for instance by discharging the magma from stage I into shallow trays placed upon cars and run into a closed chamber. If the vapors from stage I now be allowed to fiow through the cooking chamber, they will become cooled in accordance with the amount of oil volatilized from the trays. Simultaneously, they will become enriched with the oil vapors thus generated. In the drawing this step is represented by C, where the residual coke is represented as a solid mass upon .the bottom of the coking chamber.

In the third or distilling stage, the vapors from stage 2 are further cooled by admitting them tov the charging stock proper in such a manner that liquid and vapor shall be effectively commingled, thus producing distillation of the low boiling fractions. It follows that the cooled vapors drop their high boiling fractions to a very large extent and these become an integr'al part of the fluid which now becomes the raw material acted upon in the first stage. The cooling of the vapors in this distilling stage may be as low as 400 F. as the accepted fractions are far more volatile in the flow of superheated steam than when existing alone.

large flow of superheated steam commingled with" pressure blower I i, which return the freshly made steam to superheater by means of the pipe l8.

G represents the post-condenser wherein the partial condensation of the evaporator is made complete. Non-condensable gases are discharged through the vent 29, and the condensate by the pipe 30, to the separator H. From this in turn, the condensed oils are discharged by the upper pipe 32, while the water leaves by the lower pipe 34. 3| and 33, respectively, indicate the layers into which the condensate naturally separates and the junction is indicated by the double dotted lines.

The salient features of my invention are thus seen to be in the field of heat conservation. The superheated steam can be manufactured in toto without the need of a boiler plant to produce the same once the operationhas been started,

' and the residual heat residing in the vapors after the temperature has dropped toov low for cracking is used progressively for coking the residuum from cracking and for topping the charging stock. After having passed such usage, it can still be used for raising all the steam required in the process if such be desired or as much thereof as may he wanted at the will the operator.

While the cycle indicated on the flow sheet is an exceedingly advantageous way of combining the items above referred to I do not slavishly confine myself to this series of operations for it will be evident that the same can be widely varied along well known lines without interfering with the specific advantages conveyed by my invention. I will illustrate some such deviation in detail. It will be evident, that instead of returning the steam made in the operation of cooling the resultant vapors to the head of the circuit in which it was generated, it might with equal ease be passed on without compression to a simxilar unit operating under a lower pressure and this mightbe repeated many times. As the actual pressure under which an initial unit operates is almost optional, having'but little effect on steam and vapors issuing from secondly are further cooled by intimately commingling same with the incoming charging stock thus yielding two products, namely, a liquid portion consisting in part of the residual of the admixed oil and in i part of high boiling oil fractons derived from con- Meandensing vapors, and a gaseous portion consisting of superheated steam and vapors of low b:il-

ing oil fractions, said liquid portion being transferred to the cracking stage described under firstly and constituting the oil acted upon therein by the superheated steam first introduced; fourthly, a condensing stage in which the steam and vapors from thirdly are further cooled by converting the heat resident therein, both sensible and latent, into latent heat of evaporation of water, maintained out of, contact with said oil vapors and steam, at a lower pressure than that of the-condensing steam, thus condensing themixture of oil vaporsand steam and simultaneously producing a new'supply of steam at a lower pressure than that of the condensing vapors, said steam being then superheated, compressed and returned to the initial cracking stage described under firstly, thus becoming the flow of superheated steam therein specified.

2. A claim similar to claim 1, with the additive step that the distilling stage as prescribed under thirdly be carried out by scrubbing the oil vapors and steam with a controlled and re-circulated douche of its own condensate to which the new charging stock is added.

3. The method of cracking and distilling an oil which comprises: firstly, a cracking stage in which the'source of heat consists of a flow of steam superheated to the requisite temperature, admitted to the surface of a body of oil within a cracking chamber, the relative amounts of oil cracked and distilled being governed by the de gree of turbulence of the body, of oil, and yield ing two products, namely, aliquid residuum and superheated vapors; secondly, a coking stage condensing vapors, and a gaseous portion conthe products and that rather favorable than oth erwise, it follows that the compression step might be advantageously eliminated in favor of such a series as here indicated. Such modifications I therefore consider as part of my process as well as the preferred version specifically given.

Having thus fully explained my process and shown the advantages of same over the general practice of today, I claim 1. The method of cracking and distilling an oil which comprises: firstly, a cracking stage in which the source of heat consists of a flow of steam superheated to the requisite temperature and yielding two products, namely, a liquid residuum and superheated vapors; secondly, a coking stage wherein the products yielded under firstlyffurther interact with the production of a solid residuum of coke, said coke being withdrawn from the process; thirdly, a distilling stage wherein the sisting of superheated steam and vapors of low boiling oil fractions, said liquid portion being transferred to the cracking stage described under firstly and constituting the oil acted upon therein by the superheated steam first introduced; fourthly, a condensing stage in which the steam and vapors from thirdly are further cooled by converting the heat resident therein, both sensible and latent, into latent heat of evaporation of water, maintained out of contact with said oil vapors and steam, at a lower pressure than that of the condensing steam, thus condensing the mixture of oil vapors and steam and simultaneously producing a new supply of steam at a lower pressure thanithat of the condensing vapors, said steam being then superheated, compressed and returned to the initial cracking stage described under firstly, thus becoming the flow of superheated steam therein specified.

ALFRED M. 'I'HOMSEN. 

